External Memory Interfaces Intel® Cyclone® 10 GX FPGA IP User Guide

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Date 3/29/2021
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Document Table of Contents
Document Table of Contents x
1. Release Information 2. External Memory Interfaces Intel® Cyclone® 10 GX FPGA IP Introduction 3. Intel® Cyclone® 10 GX EMIF IP Product Architecture 4. Intel® Cyclone® 10 GX EMIF IP End-User Signals 5. Intel® Cyclone® 10 GX EMIF – Simulating Memory IP 6. Intel® Cyclone® 10 GX EMIF IP for DDR3 7. Intel® Cyclone® 10 GX EMIF IP for LPDDR3 8. Intel® Cyclone® 10 GX EMIF IP Timing Closure 9. Optimizing Controller Performance 10. Intel® Cyclone® 10 GX EMIF IP Debugging 11. External Memory Interfaces Intel® Cyclone® 10 GX FPGA IP User Guide Archives 12. Document Revision History for Intel® Cyclone® 10 GX External Memory Interfaces FPGA IP User Guide
2. External Memory Interfaces Intel® Cyclone® 10 GX FPGA IP Introduction x
2.1. Intel® Cyclone® 10 GX EMIF IP Design Flow 2.2. Intel® Cyclone® 10 GX EMIF IP Design Checklist
3. Intel® Cyclone® 10 GX EMIF IP Product Architecture x
3.1. EMIF Architecture: Introduction 3.2. Intel® Cyclone® 10 GX EMIF Sequencer 3.3. Intel® Cyclone® 10 GX EMIF Calibration 3.4. Intel® Cyclone® 10 GX EMIF Controller 3.5. Hardware Resource Sharing Among Multiple EMIFs 3.6. Intel® Cyclone® 10 GX EMIF Ping Pong PHY
3.1. EMIF Architecture: Introduction x
3.1.1. I/O Subsystem 3.1.2. I/O Column 3.1.3. I/O AUX 3.1.4. I/O Bank 3.1.5. I/O Lane 3.1.6. Input DQS Clock Tree 3.1.7. PHY Clock Tree 3.1.8. PLL Reference Clock Networks 3.1.9. Clock Phase Alignment
3.1.4. I/O Bank x
3.1.4.1. Implementing a x8 Interface with Hard Memory Controller 3.1.4.2. Implementing a x72 Interface with Hard Memory Controller
3.2. Intel® Cyclone® 10 GX EMIF Sequencer x
3.2.1. DQS Tracking
3.3. Intel® Cyclone® 10 GX EMIF Calibration x
3.3.1. Calibration Stages 3.3.2. Calibration Stages Descriptions 3.3.3. Calibration Algorithms 3.3.4. Calibration Flowchart
3.4. Intel® Cyclone® 10 GX EMIF Controller x
3.4.1. Hard Memory Controller 3.4.2. Hard Memory Controller Rate Conversion Feature
3.4.1. Hard Memory Controller x
3.4.1.1. Hard Memory Controller Features 3.4.1.2. Hard Memory Controller Main Control Path 3.4.1.3. Data Buffer Controller
3.5. Hardware Resource Sharing Among Multiple EMIFs x
3.5.1. I/O Aux Sharing 3.5.2. I/O Bank Sharing 3.5.3. PLL Reference Clock Sharing 3.5.4. Core Clock Network Sharing
3.6. Intel® Cyclone® 10 GX EMIF Ping Pong PHY x
3.6.1. Ping Pong PHY Feature Description 3.6.2. Ping Pong PHY Architecture 3.6.3. Ping Pong PHY Limitations 3.6.4. Ping Pong PHY Calibration 3.6.5. Using the Ping Pong PHY 3.6.6. Ping Pong PHY Simulation Example Design
4. Intel® Cyclone® 10 GX EMIF IP End-User Signals x
4.1. Interface and Signal Descriptions 4.2. AFI Signals 4.3. AFI 4.0 Timing Diagrams 4.4. Intel® Cyclone® 10 GX Memory Mapped Register (MMR) Tables
4.1. Interface and Signal Descriptions x
4.1.1. Intel Cyclone 10 GX EMIF IP Interfaces for DDR3 4.1.2. Intel Cyclone 10 GX EMIF IP Interfaces for LPDDR3
4.1.1. Intel Cyclone 10 GX EMIF IP Interfaces for DDR3 x
4.1.1.1. pll_ref_clk for DDR3 4.1.1.2. pll_locked for DDR3 4.1.1.3. pll_extra_clk_0 for DDR3 4.1.1.4. pll_extra_clk_1 for DDR3 4.1.1.5. pll_extra_clk_2 for DDR3 4.1.1.6. pll_extra_clk_3 for DDR3 4.1.1.7. oct for DDR3 4.1.1.8. mem for DDR3 4.1.1.9. status for DDR3 4.1.1.10. afi_reset_n for DDR3 4.1.1.11. afi_clk for DDR3 4.1.1.12. afi_half_clk for DDR3 4.1.1.13. afi for DDR3 4.1.1.14. emif_usr_reset_n for DDR3 4.1.1.15. emif_usr_clk for DDR3 4.1.1.16. emif_usr_reset_n_sec for DDR3 4.1.1.17. emif_usr_clk_sec for DDR3 4.1.1.18. cal_debug_reset_n for DDR3 4.1.1.19. cal_debug_clk for DDR3 4.1.1.20. cal_debug_out_reset_n for DDR3 4.1.1.21. cal_debug_out_clk for DDR3 4.1.1.22. clks_sharing_master_out for DDR3 4.1.1.23. clks_sharing_slave_in for DDR3 4.1.1.24. clks_sharing_slave_out for DDR3 4.1.1.25. ctrl_amm for DDR3 4.1.1.26. ctrl_auto_precharge for DDR3 4.1.1.27. ctrl_user_priority for DDR3 4.1.1.28. ctrl_ecc_user_interrupt for DDR3 4.1.1.29. ctrl_ecc_readdataerror for DDR3 4.1.1.30. ctrl_mmr_slave for DDR3 4.1.1.31. cal_debug for DDR3 4.1.1.32. cal_debug_out for DDR3
4.1.2. Intel Cyclone 10 GX EMIF IP Interfaces for LPDDR3 x
4.1.2.1. pll_ref_clk for LPDDR3 4.1.2.2. pll_locked for LPDDR3 4.1.2.3. pll_extra_clk_0 for LPDDR3 4.1.2.4. pll_extra_clk_1 for LPDDR3 4.1.2.5. pll_extra_clk_2 for LPDDR3 4.1.2.6. pll_extra_clk_3 for LPDDR3 4.1.2.7. oct for LPDDR3 4.1.2.8. mem for LPDDR3 4.1.2.9. status for LPDDR3 4.1.2.10. afi_reset_n for LPDDR3 4.1.2.11. afi_clk for LPDDR3 4.1.2.12. afi_half_clk for LPDDR3 4.1.2.13. afi for LPDDR3 4.1.2.14. emif_usr_reset_n for LPDDR3 4.1.2.15. emif_usr_clk for LPDDR3 4.1.2.16. cal_debug_reset_n for LPDDR3 4.1.2.17. cal_debug_clk for LPDDR3 4.1.2.18. cal_debug_out_reset_n for LPDDR3 4.1.2.19. cal_debug_out_clk for LPDDR3 4.1.2.20. clks_sharing_master_out for LPDDR3 4.1.2.21. clks_sharing_slave_in for LPDDR3 4.1.2.22. clks_sharing_slave_out for LPDDR3 4.1.2.23. ctrl_user_priority for LPDDR3 4.1.2.24. ctrl_mmr_slave for LPDDR3 4.1.2.25. cal_debug for LPDDR3 4.1.2.26. cal_debug_out for LPDDR3
4.2. AFI Signals x
4.2.1. AFI Clock and Reset Signals 4.2.2. AFI Address and Command Signals 4.2.3. AFI Write Data Signals 4.2.4. AFI Read Data Signals 4.2.5. AFI Calibration Status Signals 4.2.6. AFI Shadow Register Management Signals
4.3. AFI 4.0 Timing Diagrams x
4.3.1. AFI Address and Command Timing Diagrams 4.3.2. AFI Write Sequence Timing Diagrams 4.3.3. AFI Read Sequence Timing Diagrams 4.3.4. AFI Calibration Status Timing Diagram
4.4. Intel® Cyclone® 10 GX Memory Mapped Register (MMR) Tables x
4.4.1. ctrlcfg0 4.4.2. ctrlcfg1 4.4.3. dramtiming0 4.4.4. sbcfg1 4.4.5. caltiming0 4.4.6. caltiming1 4.4.7. caltiming2 4.4.8. caltiming3 4.4.9. caltiming4 4.4.10. caltiming9 4.4.11. dramaddrw 4.4.12. sideband0 4.4.13. sideband1 4.4.14. sideband2 4.4.15. sideband3 4.4.16. sideband4 4.4.17. sideband5 4.4.18. sideband6 4.4.19. sideband7 4.4.20. sideband8 4.4.21. sideband9 4.4.22. sideband10 4.4.23. sideband11 4.4.24. sideband12 4.4.25. sideband13 4.4.26. dramsts 4.4.27. niosreserve0 4.4.28. niosreserve1 4.4.29. ecc3: ECC Error and Interrupt Configuration 4.4.30. ecc4: Status and Error Information 4.4.31. ecc5: Address of Most Recent SBE/DBE 4.4.32. ecc6: Address of Most Recent Correction Command Dropped
5. Intel® Cyclone® 10 GX EMIF – Simulating Memory IP x
5.1. Simulation Options 5.2. Simulation Walkthrough
5.2. Simulation Walkthrough x
5.2.1. Calibration Modes 5.2.2. Abstract PHY Simulation 5.2.3. Simulation Scripts 5.2.4. Functional Simulation with Verilog HDL 5.2.5. Functional Simulation with VHDL 5.2.6. Simulating the Design Example
6. Intel® Cyclone® 10 GX EMIF IP for DDR3 x
6.1. Parameter Descriptions 6.2. Board Skew Equations 6.3. Pin and Resource Planning 6.4. DDR3 Board Design Guidelines
6.1. Parameter Descriptions x
6.1.1. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: General 6.1.2. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: FPGA I/O 6.1.3. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Memory 6.1.4. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Mem I/O 6.1.5. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Mem Timing 6.1.6. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Board 6.1.7. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Controller 6.1.8. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Diagnostics 6.1.9. Intel Cyclone 10 GX EMIF IP DDR3 Parameters: Example Designs
6.2. Board Skew Equations x
6.2.1. Equations for DDR3 Board Skew Parameters
6.3. Pin and Resource Planning x
6.3.1. Interface Pins 6.3.2. FPGA Resources 6.3.3. Pin Guidelines for Intel® Cyclone® 10 GX EMIF IP
6.3.1. Interface Pins x
6.3.1.1. Estimating Pin Requirements 6.3.1.2. DIMM Options 6.3.1.3. Maximum Number of Interfaces
6.3.2. FPGA Resources x
6.3.2.1. OCT 6.3.2.2. PLL
6.3.3. Pin Guidelines for Intel® Cyclone® 10 GX EMIF IP x
6.3.3.1. General Guidelines 6.3.3.2. x4 DIMM Implementation 6.3.3.3. Command and Address Signals 6.3.3.4. Clock Signals 6.3.3.5. Data, Data Strobes, DM/DBI, and Optional ECC Signals 6.3.3.6. Resource Sharing Guidelines (Multiple Interfaces) 6.3.3.7. Ping-Pong PHY Implementation
6.4. DDR3 Board Design Guidelines x
6.4.1. Terminations and Slew Rates with Intel® Cyclone® 10 GX Devices 6.4.2. Channel Signal Integrity Measurement 6.4.3. Layout Approach 6.4.4. Design Layout Guidelines 6.4.5. Package Deskew
6.4.1. Terminations and Slew Rates with Intel® Cyclone® 10 GX Devices x
6.4.1.1. Dynamic On-Chip Termination (OCT) in Intel® Cyclone® 10 Devices 6.4.1.2. Choosing Terminations on Intel® Cyclone® 10 Devices 6.4.1.3. On-Chip Termination Recommendations for Intel® Cyclone® 10 Devices 6.4.1.4. Slew Rates
6.4.2. Channel Signal Integrity Measurement x
6.4.2.1. Importance of Accurate Channel Signal Integrity Information 6.4.2.2. Understanding Channel Signal Integrity Measurement 6.4.2.3. How to Enter Calculated Channel Signal Integrity Values 6.4.2.4. Guidelines for Calculating DDR3 Channel Signal Integrity
6.4.4. Design Layout Guidelines x
6.4.4.1. General Layout Guidelines 6.4.4.2. Layout Guidelines 6.4.4.3. Length Matching Rules 6.4.4.4. Spacing Guidelines 6.4.4.5. Layout Guidelines for DDR3 SDRAM Wide Interface (>72 bits) 6.4.4.6. Fly-By Network Design for Clock, Command, and Address Signals
6.4.5. Package Deskew x
6.4.5.1. DQ/DQS/DM Deskew 6.4.5.2. Address and Command Deskew 6.4.5.3. Package Deskew Recommendations for Intel® Cyclone® 10 Devices 6.4.5.4. Deskew Example 6.4.5.5. Package Migration
7. Intel® Cyclone® 10 GX EMIF IP for LPDDR3 x
7.1. Parameter Descriptions 7.2. Board Skew Equations 7.3. Pin and Resource Planning 7.4. LPDDR3 Board Design Guidelines
7.1. Parameter Descriptions x
7.1.1. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: General 7.1.2. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: FPGA I/O 7.1.3. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Memory 7.1.4. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Mem I/O 7.1.5. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Mem Timing 7.1.6. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Board 7.1.7. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Controller 7.1.8. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Diagnostics 7.1.9. Intel Cyclone 10 GX EMIF IP LPDDR3 Parameters: Example Designs
7.2. Board Skew Equations x
7.2.1. Equations for LPDDR3 Board Skew Parameters
7.3. Pin and Resource Planning x
7.3.1. Interface Pins
7.3.1. Interface Pins x
7.3.1.1. Estimating Pin Requirements 7.3.1.2. Maximum Number of Interfaces 7.3.1.3. FPGA Resources 7.3.1.4. OCT 7.3.1.5. PLL 7.3.1.6. Pin Guidelines for Intel® Cyclone® 10 GX EMIF IP
7.3.1.6. Pin Guidelines for Intel® Cyclone® 10 GX EMIF IP x
7.3.1.6.1. General Guidelines 7.3.1.6.2. LPDDR3 Clock Signal 7.3.1.6.3. LPDDR3 Command and Address Signal 7.3.1.6.4. LPDDR3 Data, Data Strobe, and DM Signals 7.3.1.6.5. Resource Sharing Guidelines (Multiple Interfaces)
7.4. LPDDR3 Board Design Guidelines x
7.4.1. Terminations and Slew Rates with Intel® Cyclone® 10 GX Devices 7.4.2. Channel Signal Integrity Measurement 7.4.3. Layout Approach 7.4.4. Design Layout Guidelines 7.4.5. Package Deskew
7.4.1. Terminations and Slew Rates with Intel® Cyclone® 10 GX Devices x
7.4.1.1. Dynamic On-Chip Termination (OCT) in Intel® Cyclone® 10 Devices 7.4.1.2. Choosing Terminations on Intel® Cyclone® 10 Devices 7.4.1.3. On-Chip Termination Recommendations for Intel® Cyclone® 10 Devices
7.4.2. Channel Signal Integrity Measurement x
7.4.2.1. Importance of Accurate Channel Signal Integrity Information 7.4.2.2. Understanding Channel Signal Integrity Measurement 7.4.2.3. How to Enter Calculated Channel Signal Integrity Values 7.4.2.4. Guidelines for Calculating DDR3 Channel Signal Integrity
7.4.4. Design Layout Guidelines x
7.4.4.1. General Layout Guidelines 7.4.4.2. Layout Guidelines 7.4.4.3. Length Matching Rules 7.4.4.4. Spacing Guidelines 7.4.4.5. Layout Guidelines for DDR3 SDRAM Wide Interface (>72 bits) 7.4.4.6. Fly-By Network Design for Clock, Command, and Address Signals
7.4.5. Package Deskew x
7.4.5.1. DQ/DQS/DM Deskew 7.4.5.2. Address and Command Deskew 7.4.5.3. Package Deskew Recommendations for Intel® Cyclone® 10 Devices 7.4.5.4. Deskew Example 7.4.5.5. Package Migration
8. Intel® Cyclone® 10 GX EMIF IP Timing Closure x
8.1. Timing Closure 8.2. Timing Report DDR 8.3. Optimizing Timing 8.4. Early I/O Timing Estimation
8.1. Timing Closure x
8.1.1. Timing Analysis
8.1.1. Timing Analysis x
8.1.1.1. PHY or Core 8.1.1.2. I/O Timing
8.1.1.2. I/O Timing x
8.1.1.2.1. Read Capture 8.1.1.2.2. Write 8.1.1.2.3. Address and Command 8.1.1.2.4. DQS Gating / Postamble 8.1.1.2.5. Write Leveling
8.4. Early I/O Timing Estimation x
8.4.1. Performing Early I/O Timing Analysis
9. Optimizing Controller Performance x
9.1. Interface Standard 9.2. Bank Management Efficiency 9.3. Data Transfer 9.4. Improving Controller Efficiency
9.4. Improving Controller Efficiency x
9.4.1. Auto-Precharge Commands 9.4.2. Latency 9.4.3. Calibration 9.4.4. Bank Interleaving 9.4.5. Additive Latency and Bank Interleaving 9.4.6. User-Controlled Refresh 9.4.7. Frequency of Operation 9.4.8. Series of Reads or Writes 9.4.9. Data Reordering 9.4.10. Starvation Control 9.4.11. Command Reordering 9.4.12. Bandwidth 9.4.13. Enable Command Priority Control
9.4.2. Latency x
9.4.2.1. Additive Latency
9.4.6. User-Controlled Refresh x
9.4.6.1. Back-to-Back User-Controlled Refresh Usage
10. Intel® Cyclone® 10 GX EMIF IP Debugging x
10.1. Interface Configuration Performance Issues 10.2. Functional Issue Evaluation 10.3. Timing Issue Characteristics 10.4. Verifying Memory IP Using the Signal Tap II Logic Analyzer 10.5. Hardware Debugging Guidelines 10.6. Categorizing Hardware Issues 10.7. Debugging Intel® Cyclone® 10 GX EMIF IP 10.8. Using the Traffic Generator with the Generated Design Example
10.1. Interface Configuration Performance Issues x
10.1.1. Interface Configuration Bottleneck and Efficiency Issues
10.2. Functional Issue Evaluation x
10.2.1. Intel® IP Memory Model 10.2.2. Vendor Memory Model 10.2.3. Transcript Window Messages 10.2.4. Modifying the Example Driver to Replicate the Failure
10.3. Timing Issue Characteristics x
10.3.1. Evaluating FPGA Timing Issues 10.3.2. Evaluating External Memory Interface Timing Issues
10.4. Verifying Memory IP Using the Signal Tap II Logic Analyzer x
10.4.1. Signals to Monitor with the Signal Tap II Logic Analyzer
10.5. Hardware Debugging Guidelines x
10.5.1. Create a Simplified Design that Demonstrates the Same Issue 10.5.2. Measure Power Distribution Network 10.5.3. Measure Signal Integrity and Setup and Hold Margin 10.5.4. Vary Voltage 10.5.5. Operate at a Lower Speed 10.5.6. Determine Whether the Issue Exists in Previous Versions of Software 10.5.7. Determine Whether the Issue Exists in the Current Version of Software 10.5.8. Try A Different PCB 10.5.9. Try Other Configurations 10.5.10. Debugging Checklist
10.6. Categorizing Hardware Issues x
10.6.1. Signal Integrity Issues 10.6.2. Hardware and Calibration Issues
10.6.1. Signal Integrity Issues x
10.6.1.1. Characteristics of Signal Integrity Issues 10.6.1.2. Evaluating SignaI Integrity Issues
10.6.1.2. Evaluating SignaI Integrity Issues x
10.6.1.2.1. Skew 10.6.1.2.2. Crosstalk 10.6.1.2.3. Power System 10.6.1.2.4. Clock Signals 10.6.1.2.5. Read Data Valid Window and Eye Diagram 10.6.1.2.6. Write Data Valid Window and Eye Diagram 10.6.1.2.7. OCT and ODT Usage
10.6.2. Hardware and Calibration Issues x
10.6.2.1. Postamble Timing Issues and Margin 10.6.2.2. Intermittent Issue Evaluation
10.7. Debugging Intel® Cyclone® 10 GX EMIF IP x
10.7.1. Debugging With the External Memory Interface Debug Toolkit 10.7.2. On-Chip Debug Port for Intel® Cyclone® 10 GX EMIF IP 10.7.3. Efficiency Monitor and Protocol Checker
10.7.1. Debugging With the External Memory Interface Debug Toolkit x
10.7.1.1. User Interface 10.7.1.2. Communication 10.7.1.3. Setup and Use 10.7.1.4. Configuring Your EMIF IP for Use with the Debug Toolkit 10.7.1.5. Reports 10.7.1.6. Driver Margining for Intel® Cyclone® 10 GX EMIF IP 10.7.1.7. Example Tcl Script for Running the EMIF Debug Toolkit
10.7.1.4. Configuring Your EMIF IP for Use with the Debug Toolkit x
10.7.1.4.1. Daisy-Chaining Additional EMIF IP Cores for Debugging 10.7.1.4.2. General Workflow 10.7.1.4.3. Linking the Project to a Device 10.7.1.4.4. Establishing Communication to Connections 10.7.1.4.5. Selecting an Active Interface
10.7.2. On-Chip Debug Port for Intel® Cyclone® 10 GX EMIF IP x
10.7.2.1. EMIF On-Chip Debug Port 10.7.2.2. Access Protocol
10.7.3. Efficiency Monitor and Protocol Checker x
10.7.3.1. Including the Efficiency Monitor and Protocol Checker in Your Generated IP 10.7.3.2. Running the Efficiency Monitor with the External Memory Debug Toolkit 10.7.3.3. Communicating Directly to the Efficiency Monitor and Protocol Checker
1. Release Information
2. External Memory Interfaces Intel® Cyclone® 10 GX FPGA IP Introduction
3. Intel® Cyclone® 10 GX EMIF IP Product Architecture
4. Intel® Cyclone® 10 GX EMIF IP End-User Signals
5. Intel® Cyclone® 10 GX EMIF – Simulating Memory IP
6. Intel® Cyclone® 10 GX EMIF IP for DDR3
7. Intel® Cyclone® 10 GX EMIF IP for LPDDR3
8. Intel® Cyclone® 10 GX EMIF IP Timing Closure
9. Optimizing Controller Performance
10. Intel® Cyclone® 10 GX EMIF IP Debugging
11. External Memory Interfaces Intel® Cyclone® 10 GX FPGA IP User Guide Archives
12. Document Revision History for Intel® Cyclone® 10 GX External Memory Interfaces FPGA IP User Guide

6.3.3.4. Clock Signals

DDR3 SDRAM devices use CK and CK# signals to clock the address and command signals into the memory. Furthermore, the memory uses these clock signals to generate the DQS signal during a read through the DLL inside the memory. The SDRAM data sheet specifies the following timings:
  • tDQSCK is the skew between the CK or CK# signals and the SDRAM-generated DQS signal
  • tDSH is the DQS falling edge from CK rising edge hold time
  • tDSS is the DQS falling edge from CK rising edge setup time
  • tDQSS is the positive DQS latching edge to CK rising edge

SDRAM have a write requirement (tDQSS) that states the positive edge of the DQS signal on writes must be within ± 25% (± 90°) of the positive edge of the SDRAM clock input. Therefore, you should generate the CK and CK# signals using the DDR registers in the IOE to match with the DQS signal and reduce any variations across process, voltage, and temperature. The positive edge of the SDRAM clock, CK, is aligned with the DQS write to satisfy tDQSS.

DDR3 SDRAM can use a daisy-chained control address command (CAC) topology, in which the memory clock must arrive at each chip at a different time. To compensate for the flight-time skew between devices when using the CAC topology, you should employ write leveling.

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